Add ability to specify issues updated since a specified, dynamic date

[spascoe]

In order to reduce the load on the host Jira server, it would be very helpful to have the ability to specify on the command line, a date that would define a replacement value, usable in JQL and output file names.

Then when parsing the config YAML, would recognize '#updated' to mean replace the #updated with the value from the commandline:

For Example:
jira-agile-metrics -u '2020/03/15'

JQL: Project=foo and updated >= #10

Cycle time data: foocycle-#updated.csv